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. 2019 Mar 28;13:119. doi: 10.3389/fncel.2019.00119

Figure 1.

Figure 1

Development of action potential properties in bushy cells (BCs) and stellate cells (SCs). (A; Left) Biocytin labeling of recorded neurons reveals the BC (top) and SC (bottom) morphology, both from P14 (scale bar 25 μm). The recordings to the right, acquired from the respective cells, show the phasic firing in response to a depolarizing current step in the BC, and tonic firing in the SC. (B) The number of APs elicited by a suprathreshold current injection. Dots show the mean values for each cell obtained from >10 repetitions. Note that BCs (red) mostly generate a single AP, irrespective of age. The number of APs in SCs (blue) increases with age [the effect of age p < 0.001, two-way ANOVA]. Box-plots show medians with 25 and 75 percentiles, and interdeciles. (C) The AP half-width is shown as the mean value for each BC (red dots) and SC (blue dots; P10–11 BC n = 13, SC n = 3; P14 BC n = 6, SC n = 4; P18 BC n = 6, SC n = 6; effect of cell type p = 0.015, effect of age p < 0.001, interaction cell type × age p = 0.94; two-way ANOVA). (D) The in vivo recording position, verified by an iontophoretic injection of fluorogold. The image shows a part of a coronal slice containing the anteroventral cochlear nucleus labeled in a P14 mouse (scale bar 500 μm). (E) The repolarization slope values calculated from juxtacellular AP recordings in vivo. Red dots depict units with prepotentials (PP), i.e., BCs. Blue triangles show units with chopper firing pattern corresponding to SCs. The remaining immature units showing neither PP nor chopper firing pattern (black symbols) separate according to their slope values in the two populations. (F) Mean waveforms of extracellular APs recorded in BC (left) and SC (right) at P12, P14, and P30, normalized to and aligned at the AP maximum. Each waveform represents the average AP time course during spontaneous activity (P12: BC n = 1,274, SC n = 649; P14: BC n = 1,055, SC n = 1,251; P30: BC n = 2,524, SC n = 3,062). Discernible PP prior to the AP are characteristics of BCs, while absent in SCs. (G) Population data showing AP shortening with age and generally longer APs in BCs than in SCs (effect of cell type p < 0.001, effect of age p < 0.001, interaction cell type × age p = 0.97; two-way ANOVA). (H) Transmission delay at the auditory nerve fiber-BC synapse, measured as time between PP and AP peak (p < 0.001, one-way ANOVA; *p < 0.05, **p < 0.01; ***p < 0.001).